1. Field of the Invention
This invention relates to a fluid displacement apparatus, and more particularly, to an improvement in a thermal sensing device in a fluid displacement apparatus.
2. Description of the Prior Art
A scroll type fluid displacement apparatus is well known in the prior art. For example, U.S. Pat. No. 4,411,604 issued to Terauchi discloses a basic construction of a scroll type fluid displacement apparatus.
Generally, in the conventional refrigerant compressor, when the temperature of the refrigerant gas excessively rises, the compressor is not operating normally and increased frictional resistance between the moving parts of the compressor results. It is particularly problematic when the temperature of the refrigerant gas at the center of a scroll excessively rises, since conduction, convection and radiation cooling of the central compressor components to the atmospheric air is substantially small. One proposed solution for preventing compressor overheating employs a sensing device which terminates compression, i.e., disengages the electromagnetic clutch, when the temperature of the refrigerant gas rises above a predetermined temperature.
Referring to FIG. 1 and 2, a scroll type fluid displacement apparatus in accordance with the prior art is shown. Compressor unit 1 includes housing 10 having front end plate 11 mounted on cup-shaped casing 12. Opening 111 is formed in the center of front end plate 11 for penetration or passage of drive shaft 13. Annular projection 112 is formed in a rear end surface of front end plate 11. Annular projection 112 faces cup-shaped casing 12 and is concentric with opening 111. An outer peripheral surface of annular projection 112 extends into an inner wall of the opening of cup-shaped casing 12 so that the opening of cup-shaped casing 12 is covered by front end plate 11. O-ring 14 is placed between the outer peripheral surface of annular projection 112 and the inner wall of the opening of cup-shaped casing 12 to seal the mating surfaces therebetween.
Annular sleeve 15 is fixed to and projects from the front end surface of front end plate 11 to surround drive shaft 13 and define a shaft seal cavity. Drive shaft 13 is rotatably supported by sleeve 15 through bearing 18 located within the front end of sleeve 15. Drive shaft 13 has disk 19, at inner end thereof, which is rotatably supported by front end plate 11 through beating 20 located within opening 111 of from end plate 11. Shaft seal assembly 21 is coupled to drive shaft 13 within the shaft seal cavity of sleeve 15.
Pulley 22 is rotatably supported by bearing 23 which is carded on the outer surface of sleeve 15. Electromagnetic coil 24 is fixed about the outer surface of sleeve 15 by supporting plate 25 and is received in the annular cavity of pulley 22. Armature plate 26 is elastically supported on the outer end of drive shaft 13 which extends beyond sleeve 15. Pulley 22, magnetic coil 24 and armature plate 26 form a magnetic clutch. In operation, drive shaft 13 is driven by an external power source, for example the engine of an automobile, through a rotation transmitting device such as the above-explained magnetic clutch.
A number of elements are located within cup-shaped casing 12, including fixed scroll 27, orbiting scroll 28, and rotation preventing/thrust bearing device 35 for orbiting scroll 28. The compression chamber is defined by the inner wall of cup-shaped casing 12 and the rear end surface of front end plate 11.
Fixed scroll 27 includes circular end plate 271, wrap or spiral element 272 affixed to or extending from one end surface of end plate 271 and an internally threaded boss 273 axially projecting from the other end surface of end plate 271. Internally threaded boss 273 includes first rib portion 273a and second rib portion 273b radially facing each other and surrounding discharge port 274. Further, internally threaded boss 273 includes first notch portion 273c and second notch portion 273d radially facing each other and surrounding discharge port 274. An axial end surface of rib portions 273a and 273b are sealed on the inner end surface of bottom plate portion 121. Rib portions 273a and 273b are provided with tapped holes 254 for receiving bolts 37. Tapped holes 254 are reinforced by the wall portion therebetween. Fixed scroll 27 is secured to bottom plate 121 by bolts 37 which screw into tapped holes 254. In this manner, fixed scroll 27 is secured within the inner chamber of cup-shaped casing 12.
Circular end plate 271 of fixed scroll 27 partitions cup-shaped casing 12 into front chamber 29 and rear chamber 30. Seal ring 31 is disposed within a circumferential groove on circular end plate 271 to form a seal between the inner wall of cup-shaped casing 12 and the outer surface of circular end plate 271. Spiral element 272 of fixed scroll 27 is located within front chamber 29.
Cup-shaped casing 12 has a fluid inlet port 36 and a fluid outlet port 39, which are connected to rear and front chambers 29 and 30, respectively. Further, cup-shaped casing 12 is provided with sensor pocket 122 in which thermal sensor 60 is disposed. Thermal sensor 60 terminates compression when the temperature of the refrigerant gas exceeds a predetermined value. The compressed refrigerant gas strikes against thermal sensitive area 123 formed on inner surface of cup-shaped casing 12 corresponding to the bottom of sensor pocket 122. A hole or discharge port 274 is formed through circular end plate 271 at a position near the center of spiral element 272. Retainer 50 and read valve 38 are fixedly secured to circular end plate 271 by bolt 51. Reed valve 38 closes discharge port 274 when the pressure in discharge chamber 30 exceeds the pressure in the central fluid pocket.
Orbiting scroll 28, which is located in front chamber 29, includes circular end plate 281 and wrap or spiral element 282 affixed to or extending from one end surface of circular end plate 281. Spiral elements 272 and 282 interfit at an angular offset of 180.degree. and at a predetermined radial offset. Spiral elements 272 and 282 define at least one pair of sealed off fluid pockets between theft interfitting surfaces. Orbiting scroll 28 is rotatably supported by bushing 33 through beating 34 placed between the outer peripheral surface of bushing 33 and the inner surface of annular boss 288, which axially projects from the end surface of circular end plate 281. Bushing 33 is connected to an inner end of disk 19 at a point radially offset or eccentric to the axis of drive shaft 13.
Rotation preventing/thrust bearing device 35 is disposed around the outer peripheral surface of boss 288 and placed between the inner end surface of front end plate 11 and the end surface of circular end plate 281. Rotation preventing/thrust bearing device 35 includes fixed ring 351 attached to the inner end surface of front end plate 11, orbiting ring 352 attached to the end surface of circular end plate 281, and a plurality of bearing elements, such as balls 353, placed between the pocket formed by tings 351 and 352. Rotation of orbiting scroll 28 during orbital motion is prevented by the interaction of balls 353 with tings 351, 352. The axial thrust load from orbiting scroll 28 also is supported on front end plate 11 through balls 353.
With reference to FIG. 2, the compressed refrigerant gas exhausted from discharge port 274 flows radially, outwardly and branches into two flows paths. One flow path is through first notch portion 273c and a second flow path is through second notch portion 273d as shown by the arrows in FIG. 2. The separate flow paths flow along the inside surface of cup-shaped casing 12 and merge at fluid outlet port 39. From there, the compressed refrigerant gas is delivered to other components in the air conditioning circuit, e.g., a condenser.
The temperature of the compressed refrigerant gas is measured by thermal sensor 60 disposed in sensor pocket 122. Thermal sensor 60, however, only senses the temperature of the refrigerant in one of the two flow paths, that which flows through second notch portion 273d. The refrigerant flowing through the second flow path (through first notch portion 273c) essentially avoids contact with thermal sensitive area 123. Consequently, there is a difference between the actual temperature of the compressed gas and the temperature sensed by thermal sensor 60. As a result, it is considerably difficult in this arrangement to approximate the actual temperature of the compressed gas.